Tractor-trailer combinations may include a truck tractor coupled to pull one or more trailers. The trailer or trailers have various electrical systems (e.g., brake and running lights) that are powered by the tractor electrical system. An electrical cable is connected between the tractor and trailer to supply tractor electrical power to the trailer. A cable connector mounted on the tractor (or trailer) provides a socket to receive a plug of the trailer electrical cable. The cable connector is typically connected to a tractor wiring cable and is mounted on the rear of the truck tractor. The cable connector may be fixed to a bracket mounted to the back of the cab.
A tractor/trailer electrical connector device must meet the SAE J560b (Americas) or ISO 3731 (Europe) connection system standard, which specifies the physical terminal locations and electrical configurations. The standard also specifies that the connector have a cap with a mechanism to lock the trailer electrical cable to the connector to resist inadvertent trailer cable disconnects.
An example of this connection device that is in common use in the industry and available from Phillips Industries is shown in U.S. Pat. No. 6,743,025 to Howard. The sole figure shows a device having socket 10 that includes a barrel 13 supporting terminal pins 14. The barrel is received in a plug 60. The plug carries connectors 17 to connect the terminals 14 with a wiring harness. A flange 18 on the socket and a flange 22 on the plug overlap and are fastened to a wall of the tractor or trailer. A cap 19 as required by SAE J560b is shown in a closed position.
A second example is the device shown in U.S. Pat. No. 6,450,833 to Brown, Jr. et al. A trailer electrical cable plug 26 is shown inserted in the socket 122. As seen in FIG. 9, this device includes a cap 134 and a wedge shaped locking tab (not numbered) may be seen on the inner surface of the cap engaging a tab (also not numbered) on the plug 26. This interlocking tab arrangement is common in the industry.
This cap lock system is designed to keep the trailer electrical cable plug locked into the cab electrical socket, and is intended to allow the cable plug and the connector socket to disengage, or breakaway, when the vehicle pulls away from the trailer with the cable still connected. By disengaging, the cap locking tab will not resist the cable plug pulling out of the socket and the plug and socket can separate without damage to either. In practice, however, this locking mechanism does not always release the trailer connector plug and socket when the vehicle pulls away. The cable may pull the connector from its mounting if the locking mechanism does not release, and the connector, the bracket, and the cab wall may be damaged.
Another issue with the existing or known connector ‘breakaway’ solutions is they have a terminal connection system to connect the connector device to the tractor wiring harness. This added connection system adds voltage drop that may not be acceptable for a long trailer configuration such as a triple trailer. This voltage drop will also increase over time due to thermodynamics, material migration, or due to multiple disconnects. Once the voltage drop becomes too high, the system will not be able to provide the power needed for certain applications such as illumination of the tail lights.